Recently, an organic electroluminescent display (organic EL display) is being actively developed as an image display apparatus. The organic EL display is, unlike a liquid crystal display or the like, a so-called self luminescent type (or kind of) display which embodies display through light emission of a luminescent material including an organic compound in an emission layer by recombining holes and electrons injected from an anode and a cathode in the emission layer.
An example of an organic electroluminescent device (organic EL device) includes an anode, a hole transport layer disposed on the anode, an emission layer disposed on the hole transport layer, an electron transport layer disposed on the emission layer and a cathode disposed on the electron transport layer. Holes are injected from the anode, and the injected holes are injected via the hole transport layer into the emission layer. Meanwhile, electrons are injected from the cathode, and the injected electrons are injected via the electron transport layer into the emission layer. The holes and the electrons injected into the emission layer are recombined (or combined), and excitons are generated in the emission layer. The organic EL device emits light using light generated by the radiation deactivation of the excitons. The organic EL device is not limited to the aforementioned configuration, but many modifications thereof are possible.
For the application of an organic EL device in a display, the organic EL device should have high efficiency and long life. For example, in a blue emission region, the driving voltage of the organic EL device is high and the emission efficiency thereof is undesirable or insufficient when compared to a green emission region and a red emission region. To realize the high efficiency and the long life of the organic EL device, the normalization, the stabilization and the increase of the durability of a hole transport layer are examined.
As a hole transport material used in a hole transport layer, various suitable compounds such as an aromatic amine compound have been used, however tasks concerning the life of a device remain. As favorable materials for the increase of the life of the organic EL device, an amine derivative substituted with, for example, an aryl group or a heteroaryl group was suggested. However, an organic EL device using the above-mentioned materials has undesirable or insufficient emission life. Thus, studies on an organic EL device having increased emission life are continuously required.